The coolant doesn't get cooled "twice" it just gets cooled longer. Given two radiators, one vertical and the other cross-flow of the same cross-sectional area, you're proposing a "6 of one, 1/2 dozen of the other" scenario, since, in the cross-flow you have 1/2 the # of tubes at a time being used for twice the distance. Any other way, more tubes or different cross-section and your comparing apples with oranges. In such a case you can't state that one style is better than the other, just different. With either style, you have to follow the "rules."

The problem with cross-flows and their longer tube length, as I see it, is there's greater resistance to coolant flow (based on a phenomena called Reynolds number) and a greater possibility for increased resistance, pressure drop and then aeration.

The auto mfgs went to cross-flow radiators to lower the hood line for styling purposes not because it's a new or better technology.

Since you're doing a one-off installation of the 8V92 in the Scenicruizer, I'd pay careful attention to the conformation of the installation. By that I mean the choice of components and their orientation to eachother. Keep internal coolant flow restriction down and pay attention to minimize aeration.

The "old" vertical style had a benefit in that the top tank did provide for some de-aeration, although there's much better methods and approaches to do that.

For the "record" Cooling the heads first is the better approach, especially in a wet sleeve engine like the 8V92, as it cools better and, at the same time, keeps the sleeve size more constant and improves the sleeve seal performance. This ain't conjecture, actual test and implementation proved it years ago.

As stated by Marc, electric fans would not be enough cooling for the air to air intercooler. If you have removed the bus A/C and still have the right engine hatch free, that would be a good place for the air to air cooler running an engine driven fan off what used to be the compressor drive. Three ways to drive it-first is just running all the time, but then it could overly cool the engine in winter type weather. Then there is a themostatically controlled fan hub that comes up to speed around 200 degrees. Course the most sophisticated would be to use an air operated fan clutch with the thermostat on the intake air to come on above 150 degrees. But I agree that the mechanically driven fan is the way to go.Personally, I drive mostly in warm weather, so I'll stay with my direct drive constantly on radiator fan. Good Luck, TomC

I want to add that a cross flow radiator is gonna have to have an Aspirator included in the build up of the system. An Aspirator is a device used to remove entrapped air in the radiator. Research this, you will have to have one.

Also you will have to construct a bypass restriction to keep enough pressure for engine deaeriation and to make the Aspirator function to work correctly.

Aeration is the enemy here. The cross flow system IMHO has a higher chance of aeration becoming a problem and that ain't good on a wet sleeve engine.

More accurately, the Aspirator (De Aerator) helps remove air trapped in the coolant. All pressurized cooling systems have trapped air. As long as the air remains out of suspension in the coolant (bubbles) the coolant retains the best ability to cool the engine.

A properly designed Deaerator will not only separate out the bubbles, but have features to block re-aeration at the same time. Them durn bubbles are relentless!

'The bubbles in the coolant are tiny insulators and restrict the ability for the coolant to pick up heat - more than the drop in temperature of the mass of the (mister cooled) coolant increases the POTENTIAL for the coolant to absorb more heat (which it would if it werent for the "tiny bubbles")"

This was expressed awkwardly.

Bubbles restrict the coolant from picking up heat. For a given mass of coolant (let's say a gallon, with bubbles), reducing the coolant temperature 10% by spraying the radiator with misters is meaningless if the continued presence of the bubbles drops the ability of the coolant to pick up that heat by a factor of 20% (numbers for example only). Misters only cool the coolant, they don't remove the bubbles, only de-aeration removes the bubbles.

The bubbles totally overcome the small benefit of reducing the temp of the coolant by 10%.

Most commercial cooling systems already have some sort of de-aerator. Just look at the top of the radiator and the top of the engine and if you see small lines coming off them going to the overflow tank, you have it. I know I have one line coming off the top of my radiator (down flow) and another coming off the top of my thermostat housing (I have a single thermostat housing with two thermostats in it rather than one on each side since mine is a laid over V drive). Good Luck, TomC

TomC points out a simple and effective method of removing aeration at "major points". There's a host of minor points that contribute to the problem as well. All DD 2 stroke engines have multiple minor points.

There's all sorts of devices of increasing complexity and expense that reduce coolant aeration, including more hoses and a dedicated de-aerator column.

Regardless of all these devices, the absolute, basic, minimum-requirement is reducing the flow restriction in the "radiator" section of the system.

The bean counters are always in a fight wth the engineers and only give the minumum radiator necessary. This gets restricted due to poor maintenance and (virtually) no amount of de-aeration is gonna cure the problem(s). The system, due to the laws of physics, will produce more air than can be extracted.

I had a lot of trouble keeping my 8V92 warm in cold weather. Below 32 degrees. I had to keep a throw rug up against the actual radiator core and it still would only get up to about 160 degrees. That is why I was under the impression that shutters were to try and resolve this problem.Richard

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Our large 30K & 40K lumber lifts have the shutter set up on them. Just as you describe they have problems making heat in the winter. The shutters get stuck open in the summer from the lumber yard dirt and mud. Then I have to listen to the lift drivers cry in the winter when they have no heat.

Richard- you are correct. Especially with the older thermostat designs before they came out with shutterless cooling in the 80's. Even so, I also used a winter front on my truck below 40 degrees to keep the heater pushing hot air. Now, with air to air intercooling on all Diesels, it is important that you not cover up the entire radiator. Typically you'll see winter fronts with some sort of hole in it so some air gets through all the time. To bad you couldn't have some sort of fan clutch on those squirrel cage blowers. I know the newer MCI's with the big radiators with conventional type fans do have air clutches on them. But on trucks, you have to contend with ram air. And you can imagine how cold mere 40 degrees at 75mph can really be. Good Luck, TomC

OK, here's a hypothetical situation- a person has a MC8 (or any bus for that matter) and has no cooling system components. No fans, radiators, and no bracketry or mounts built to hold existing components. So, its not like bolting in MCI rads or fans, etc. With a 8V71TA or 8V92T (similar cooling requirements) How would a person proceed to design a cooling system that will do the job without band aids? Bernhard bus mounts conventional radiator in MCI at engine level on the drivers side, similar to Eagle or Prevo. Heres a linkhttp://www.bernhardbus.com/Step%202.htm A hydraulic or mitre box fan wouldnt be difficult- What size radiator did 8V92 Highway trucks use, and did that system experience overheating problems similar to the same engine in bus applications? Do the Eagle and Prevo's with 8V92 have cooling system problems as well?

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OK, here's a hypothetical situation- a person has a MC8 (or any bus for that matter) and has no cooling system components. No fans, radiators, and no bracketry or mounts built to hold existing components. So, its not like bolting in MCI rads or fans, etc. With a 8V71TA or 8V92T (similar cooling requirements) How would a person proceed to design a cooling system that will do the job without band aids? Bernhard bus mounts conventional radiator in MCI at engine level on the drivers side, similar to Eagle or Prevo. Heres a linkhttp://http://www.bernhardbus.com/Step%202.htm A hydraulic or mitre box fan wouldnt be difficult- What size radiator did 8V92 Highway trucks use, and did that system experience overheating problems similar to the same engine in bus applications? Do the Eagle and Prevo's with 8V92 have cooling system problems as well?

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Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming: WOO HOO, what a ride

My 8V-92TA in my truck had a 1,360 sq in copper/brass down flow with 5 row. When loaded to 80,000lb, like clockwork would pull the grapevine southbound (5 miles of 6% grade over 100 degrees in summer) at 28mph at 2,100rpm. You aren't getting much ram affect at 28mph, so the constant on fan did the trick. Always was and am vigilant about watching water temp. If it got critical, would slow down and grab another gear and go up a bit slower (but never shut off the A/C). So pretty much the sizing of the radiators on trucks would be the same on buses, just that a buses fan would run more if not continuously. I know Freightliner sizes their radiators for worse case senario-mainly stop and go traffic (less than 20mph) in 100 degree weather. That's the reason that when an Allison is requested, the horsepower is derated to 455hp on Series 60 and 410hp on the Mercedes-Benz and Cat C13, but still with 1550lb/ft torque. Good Luck, TomC

You're making alot of work for yourself tossing all the MCI bracketry. If you compare a 8V71TA to a 8V92TA, is the 92 derated to 400HP?

I think if the stock MCI 8V92 setup were in place, radiators serviced (no buildup) and you paid some attention to de-aeration, you wouldn't have a problem. If it overheating kept up, I'd test the system for flow resistance and correct that. If it still kept up I'd get aggressive with de-aeration and maybe some non-standard modifications. Getting agressive with de-aeration conteplates some engine disassembly and is best attempted with the engine out of the bus. I'll be going straight to aggressive as I'm about to start assembling my 8V92.

But is is quite possible that the basic MCI system can be made to work without the effort to re-engineer and fabricate a "new" setup.

Most efficient, both effort and cost wise, from my point of view, is to follow these steps in order.

It was just hypothetical. I haven't even removed a hose clamp. But my radiators are the stock MC8 units for 8V71N and Allison auto.

I'm just considering all the alternatives and using the board members combined practical experience and well as opinions to try to figure what is the best approach to deal with the cooling system. If a person does research on the BBS systems, they'll see that one of the most common mechanical issues with MCI buses is the inadquate engine cooling system. The only folks who are making improvements to these 30 year old machines is bus enthauisists; so for every improvement that has been made, someone had to scratch their head and consider the possibilities of using the modern materials available today or alternative applications and how they can be incorporated to improve the operation of the machine. Just as the wandering steering issue was "solved" by the application of intregal steering boxes to the older coaches, it is possible there could be a similar improvment in the cooling system. Of course, a person could buy the intregal box from MCI and pay top dollar for the parts and then pay to have it installed. Fred Hobe figured out what truck application will work and how to do the work oneself, and it makes the same improvement for much less $$$. Of course, I can do the MCI type route with the larger 102 radiators and spend the $2000 (est).....And I'm certainly not knocking that route,as I will probably take it aslo. But if folks like Fred did that without considering and evaluating the other possibilities, the bus communitty would not have the lower price oprion that works just as well. I changed my steering to intregal using Fred's method and instruction and its awesome the improvement in pleasure to drive and saved a lot of dough that I used on something else on the bus. Thanks Fred. Part of the fun and challenge of owning a bus and doing the conversion myself is to figure out what can be done. There's nothing on my bus thats cutting edge..but I think there are many small neat things that I have mostly gathered info from here and there and applied that info to my project. I don't know a lot about cooling engineering. But there are folks here that do.....sometimes it takes a conversation like this one to ferret out those opinions and suggestions and then maybe they can combine to shed some new light on an old problem......thanks to all who have contibuted to this thread.......we can collectively take the info and consider the possibilities. Chuck Lott

« Last Edit: July 23, 2006, 01:22:31 PM by ChuckMC8 »

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Far better is it to dare mighty things,to win glorious triumphs,even though they may be checkered by failure, than to rank with those poor spirits who neither enjoy nor suffer much,because they live in the gray twilight that knows neither victory nor defeat. Theodore Roosevelt (1858-1919)